Pressure gauge construction

ABSTRACT

Excess pressure being supplied to a pressure gauge is controllably relieved through the gauge cavity and an unsealed aperture in a spring-like crystal. A sleeve member extends transversely in a forced engagement between the inside face of the crystal and an annular gasket compressed in surrounding relation about the inlet of the Bourdon tube. The gasket normally seals the passage clearance about the tube inlet against supply pressure leakage therepast but in response to an overpressure is displaced inwardly toward the cavity until leakage can occur. Concomitant displacement of the sleeve member deflects the crystal outwardly a like amount afforded by its spring rate matched in correlation with the maximum anticipated overpressure to be provided for.

This application is a continuation-in-part of application Ser. No. 908,482 filed May 22, 1978, now U.S. Pat. No. 4,161,888 .

TECHNICAL FIELD

The field of art to which the invention pertains comprises the art of measuring and testing as related to fluid pressure gauges.

BACKGROUND OF THE INVENTION

Pressure gauges enjoy very extensive commercial and industrial use and are consequently regarded as high production items. Because of such wide use, they are supplied by a plurality of manufacturers and sold in very price conscious competition. Each manufacturer instinctively strives to reduce product costs by improvements, however marginal, which reduce labor and/or materials that can contribute to cost savings in the end product.

Commonly affording pressure sensitivity in the pressure gauge is a Bourdon tube of a pressure-tight construction having a free end displaceably movable in a well known and predictable manner in response to pressure changes supplied at its inlet. To translate tube movement into values of pressure, a pointer is displaceably driven by its free end opposite calibrated dial plate. For ensuring readout accuracy, provision is usually made for calibrating the pointer to the zero position of the dial.

In most conventional gauge constructions, the inlet end of the Bourdon tube is secured to a stem connection extending outward of the casing either rear or bottom. In the back connected version the dial plate can be rotatably positioned in the course of assembly relative to the socket to effect the zero adjustment without detrimentally affecting the assembly. This is not possible, however, in the lower or bottom connected design since the dial plate aligns with the socket and cannot be adjusted. It has also been known to rotate the coil/pointer/crystal as a unit in effecting the zero calibration by use of a crystal construction as disclosed, for example, in U.S. Pat. No. 3,952,598. The latter has been found particularly suitable and economically advantageous as a manufacturing adjustment for a relatively small diameter fire extinguisher type gauge in which the pointer is directly supported on the free end of the coiled Bourdon tube. Such constructions, however, do not permit post-assembly calibration. Moreover, they generally expose the Bourdon tube and appearance-wise are marketably unsuitable for larger diameter, conventional type gauges in which only the pointer is usually visible through the crystal while the Bourdon tube and movement, if any, are concealed. It has therefore not been known how to construct a zero adjustment on such gauges capable of utilization either during or post-assembly while being equally suited for either a lower or back connected socket construction. Despite recognition of the problem, a ready solution has not heretofore been known.

SUMMARY OF THE INVENTION

This invention relates to a pressure gauge construction and more specifically to a coil/pointer unit type zero adjustment affording an otherwise conventional appearance for a gauge construction while being equally suited for either back or lower connected stem versions. This is achieved in accordance herewith by use of a central shaft which extends laterally inward of the casing from a supportive centering flange on the inside face of the crystal. An internal hex formation in the shaft end is accessible through a normally covered aperture in the crystal. The other end of the shaft terminates behind the dial face and supports a coiled Bourdon tube rotationally secured thereto. A more or less U-shaped pointer unit is supported on the shaft via a bored center rotationally free thereof. The unit includes a front leg simulating a pointer that is positioned on the shaft forward of the dial face while the remainder is positioned behind the dial face operationally connected with the free end of the Bourdon tube. Inserting a tool through the crystal aperture enables arcuate displacement of the shaft which in turn zero adjusts the pointer. After zero calibration has been completed, the crystal aperture can optionally be closed by whatever cover unit is being employed. Since the dial face per se is not displaced, the adjustment feature is equally suited for either lower or back connected stem constructions. At the same time the gauge outwardly has a conventional gauge appearance while utilizing the economically viable coil/pointer zero adjustment feature which has proven more economical than prior art constructions utilized for those purposes. Moreover, by virtue of this construction utilizing a crystal with predetermined spring rate properties, excess pressure being supplied can be relieved through the gauge cavity and the crystal aperture.

It is therefore an object of the invention to provide a novel coil/pointer zero position setting apparatus for a pressure gauge.

It is a further object of the invention to effect the previous object in an efficient and economical manner with a construction equally suited for either a lower or back connected gauge version.

It is a still further object of the invention to provide a novel pressure relief construction for a pressure gauge.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a front elevation of a pressure gauge construction in accordance herewith;

FIG. 2 is a sectional view taken substantially along the lines 2--2 of FIG. 1;

FIG. 3 is a fragmentary alternative socket construction to that shown in FIG. 2;

FIG. 4 is a fragmentary enlargement of the boxed outline 4 of FIG. 2; and

FIG. 5 is an exploded isometric view of the zero adjustment components of the previous FIGURES.

Referring now to FIGS. 1, 2, 4 and 5 of the drawings, the gauge construction in accordance herewith comprises a transparent plastic crystal 10 of clear polycarbonate which attaches via a snap connection 12 to a molded plastic back unit 14 to form a casing. Connection 12 also retains crystal 10 against blowout as will be described. Integrally part of back unit 14 is a lower extending stem 16 which is threaded at 18 for system mounting and defines an inlet passage 20 through which to receive system pressure "P" to be measured. A dial plate 22 containing inscribed graduations of pressure values 24 is secured seated between an annular flange 26 of the backing unit and an annular shoulder 28 of the crystal. In this position the dial plate serves to divide the internal casing cavity between a front portion 30 visibly exposed through the crystal and a rear portion 32 generally concealed from view. Values of pressure are indicated by a pointer 42 that is operationally displaced by pressure induced deflections of a Bourdon tube 44.

For effecting zero calibration settings in accordance herewith, crystal 10 includes a small diameter centrally located aperture 34 extending between an external recess 36 and an internal counterbore 38. Normally, a detachable dusttight but otherwise unsealing plug or tape 37 is contained in recess 36 to maintain the interior free of dust. A circular boss 40 surrounds the counterbore 38 and provides support for end 51 of an essentially stationary shaft 50 that includes a female wrench hex socket 58. Shaft 50 extends transversely through an aperture 23 in dial plate 22 and behind the dial plate merges with an integral larger diameter tubular sleeve 60 terminating at an end 72. End 72 is adapted to be received in back unit cup flange 68 having a bore 70 that via recess 66 communicates with laterally extending inlet passage 20. Sleeve 60 is radially surrounded by the flat, spiral wound coiled portion of Bourdon tube 44 and includes an axial slot 62 embracing the coil before it incurs a right angle bend as disclosed, for example, in U.S. Pat. No. 3,952,598. Beyond the bend within sleeve 60, the Bourdon tube converts to a tubular cross section extending to its inlet end 64 received in recess 66 which is in open communication with inlet passage 20. When assembled in the manner illustrated, the face of sleeve end 72 engages a metal washer 74 to in turn compress an O-ring gasket 76. This effects a pressure-tight seal about the Bourdon tube thereat preventing leakage of supply pressure into the casing cavity except for overpressure relief as will be explained.

Pointer 42 for purposes hereof is radially connected and preferably integrally molded of metal or plastic to a tubular sleeve 46 supported for rotation via a through bore 48 about shaft 50. Longitudinally with shaft 50, sleeve 46 extends axially through dial plate aperture 23 and at its opposite end includes an integral or attached radial arm 52 containing a radial slot 54. Laterally received in the slot operationally linking pointer 42 to Bourdon tube 44 is a lateral pin 56 secured to the free end of the Bourdon tube. For that purpose, slot 54 is of a length sized to permit unrestrained displacement of the coil in the course of normal expansion and contraction.

In the alternative stem construction of FIG. 3, the integral stem 16 is replaced with a two-component stem 80 affording a metal connector 84 when required by a customer. For this purpose plastic stem 16 is shortened and includes a threaded counterbore at 82 to receive a metal threaded insert 84 having a thrubore 85. When assembled in the manner shown, O-ring gasket 86 is compressed to provide a pressure-tight seal thereat.

In a preferred embodiment, crystal 10 is constructed so as to accommodate excess pressure imposed by inlet pressure "P" against O-ring gasket 76 by deflecting outward to the relation shown dashed in FIG. 4. The value of excess pressure to be provided for is usually at about one-half the burst pressure of the Bourdon tube coil 44 and is effected by a crystal deflection distance "X" sufficient to displace O-ring seal 76 inward of the casing cavity. This permits leakage past the seal into the cavity and then outward of unsealed aperture 34 and/or other leak paths in the casing. Snap connection 12 must be sufficiently effective during periods of crystal deflection to retain crystal 10 against blowout.

For utilizing crystal 10 in this manner, the deflection distance "X" as will enable O-ring seal 76 to be dislodged sufficiently to permit leakage of a pressure "P" will vary with the spring rate "K" of the crystal and the face area "A" of seal 76. The spring rate "K" can then be determined by the following relationship:

    K=PA/X

For an "X" of about 0.030 inches, an "A" of about 0.030 square inches and an intended relief pressure of about 1000 p.s.i. the required spring rate "K" is about 1000 lbs/inch. This can then be provided for with an appropriate crystal thickness "t" correlated to the properties of the crystal material. In some instances it may be preferable to provide the required spring rate at some elevated temperature such as at 300° F. to afford pressure relief in the event of fire or explosion. Under those circumstances, relief pressure at room temperature would be significantly higher.

In operation zero setting in accordance herewith is effected by detaching tape or cover 37 as to render the tool receiving hex formation 58 externally accessible through crystal aperture 34. A hex wrench 78 (FIG. 5) is then placed through aperture 34 into shaft socket 58 for rotating shaft 50. Rotating shaft 50 in this manner has the effect of rotating Bourdon tube 44 which through pin connection 56 and arm 54 effects a corresponding rotation of the pointer 42. In this manner, on-site and in-service zero calibration can be readily made whenever required by the consumer without any disassembly of the instrument and without regard to whether the gauge includes a back or bottom stem connection. Moreover, by appropriately matching the crystal spring rate properties with a contemplated value of overpressure in a system supply to the gauge, the crystal aperture can afford pressure relief by means of crystal deflection permitting O-ring 76 to unseal.

By the above description there has been disclosed a novel construction for a pressure gauge which appearance-wise closely simulates accepted marketing standards for such gauges while at the same time readily affording a coil/pointer zero adjustment capable of ready in-service setting equally suited for either lower or back connected stem constructions. Since essentially all operating components when assembled as above other than pointer 42 are contained in rear cavity 32, the entire gauge construction simulates a conventional appearance for gauges of this type. That is, with pointer 42 being the only visible component by virtue of its intervening relation between crystal 10 and dial plate 22, the operating mechanism in rear portion 32 remains essentially concealed from view through the crystal. These results are therefore achieved by a relatively simple arrangement of components of comparably less construction cost than conventional gauges yet affording all the virtues thereof. Consequently, such gauges can be manufactured at considerably less cost than similar purpose gauges of the prior art as to afford substantial marketing advantage thereover in meeting a long-time objective of the industry. Moreover, should an excessive supply pressure be encountered, the construction hereof affords a ready relief through the gauge cavity and the crystal aperture without any additional fabrication cost being attributed thereto.

Since many changes could be made in the above construction and many apparently widely different embodiments of this invention could be made without departing from the scope thereof, it is intended that all matter contained in the drawings and specification shall be interpreted as illustrative and not in a limiting sense. 

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:
 1. A pressure relief construction for a pressure gauge comprising in combination:(a) a hollow casing at least partially defined by a transparent viewing crystal and having at least one predetermined pressure leak path extending between the interior cavity and the exterior thereof; (b) an inlet passage defined through said casing and adapted for connecting to a source of fluid pressure to be measured; (c) a Bourdon tube generally contained within the cavity of said casing having its inlet positioned extending into said inlet passage with a defined clearance therebetween; (d) seal means normally positioned for sealing the clearance between the Bourdon tube and the inlet passage wall thereat when fluid pressure at said Bourdon tube inlet is below a predetermined maximum value and displaceable toward said cavity to unseal said clearance in response to fluid pressure at said inlet exceeding said predetermined maximum value; and (e) spring means acting against said seal means urging said seal means into its said normal position, said spring means having a spring rate correlated to said predetermined maximum value of fluid pressure to permit said displaceable unsealing of said seal means when said predetermined maximum value of fluid pressure is exceeded at said inlet.
 2. A pressure relief construction for a pressure gauge according to claim 1 in which said pressure leak path comprises an aperture extending through said casing.
 3. A pressure relief construction for a pressure gauge according to claim 2 in which said pressure leak path aperture extends through the crystal of said casing.
 4. A pressure relief construction for a pressure gauge according to claims 1, 2 or 3 in which said spring means comprises said crystal and there is included transmitting means in intermediate engagement between the interior of said crystal and said seal means for transmitting the acting spring force of said crystal against said seal means.
 5. A pressure relief construction for a pressure gauge according to claim 4 in which the surfaces of said crystal and said seal means engaged by said transmitting means are generally parallel and said transmitting means extends transversely therebetween.
 6. A pressure relief construction for a pressure gauge according to claim 5 in which said crystal is characterized by outward deflection in response to said displaceable unsealing of said seal means.
 7. A pressure relief construction for a pressure gauge according to claim 6 in which said seal means comprises an annular gasket encircling a portion of said Bourdon tube in the vicinity of the tube inlet.
 8. A pressure relief construction for a pressure gauge according to claim 6 in which the spring rate of said crystal is correlated to said predetermined maximum value of fluid pressure at a predetermined elevated temperature of said crystal. 